Hydroforming Unit

ABSTRACT

A hydroforming unit comprises a mould ( 19,20 ) that can be opened and sealing arrangements ( 30 - 33; 35 - 39 ) for sealing the ends of a tube-formed blank ( 16 ) placed in the mould, each one of the sealing arrangements ( 30 - 33; 35 - 39 ) comprises a ring ( 30, 35 ) with a thin wall that fits into the inner surface of the tube ( 16 ), and a plug ( 33, 36 ) that can be displaced in an axial direction mounted axially inside of the ring, and an arrangement ( 32,37 ) for initially drawing the plug ( 33, 36 ) outwards to put the ring under elastic tension against the inside of the tube-formed blank so that the plug and the ring together form a seal.

TECHNICAL AREA

The invention relates to a hydroforming unit comprising a mould that can be opened and sealing arrangements for sealing the ends of a tube-formed blank placed in the mould.

THE PRIOR ART

In static hydroforming, high pressures are used for cold shaping of blank into a product. Closed tube-formed blanks are often used, which have an inlet for a pressure medium. When open tube-formed blanks are used together with releasable sealing arrangements for sealing off the ends, the forces exerted on the end sealings will be very big and the sealing arrangements must therefore be heavy and clumsy.

AIMS OF THE INVENTION

The aims of the invention are to provide a simplified sealing arrangement for a tube-formed blank in a hydroforming unit.

BRIEF DESCRIPTION OF THE INVENTION

The aim described above is achieved when each one of the sealing arrangements comprises a ring with a thin wall that fits into the inner surface of the tube, and a plug that can be displaced in an axial direction mounted axially inside of the ring, at least one of the ring and the plug having a conical form such that the plug and the ring together form a seal that is self-locking inside of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically and seen from the side a production line according to the invention.

FIG. 2 shows the same production line seen from above.

FIG. 3 shows an enlargement of a part that is shown in the preceding drawings.

DESCRIPTION OF PREFERRED AND ILLUSTRATED EMBODIMENT

The drawings show a decoiler 11 for unrolling a steel strip 12 from a coil 13. The strip is led through a roll-forming unit 14 with shaping rollers 15, shown schematically. The strip is folded successively in the roll-forming unit to a tube 16, the longitudinal seam of which is welded together by a welding unit 17 when the tube passes the stationary welding unit. The tube may have a circular cross-section as shown. The roll-forming unit constitutes also the feed arrangement for the steel strip.

A hydroforming unit 18, shown schematically, is located after the welding unit. The hydroforming unit has a mould that consists of two moulding parts, an upper part 19 and a lower part 20. The mould is shown closed in FIG. 1 and it can be opened by machine power through the lower part being displaced downwards as is shown by the arrow 21 and the upper part being displaced upwards as is shown by the arrow 22 in FIG. 3. The mould parts are not shown in FIG. 2, but their inner shape is indicated.

When the tube 16 has been formed, the mould 19, 20 is held open such that the product 23 formed in the preceding manufacturing cycle can be removed from the mould while at the same time the tube 16 is continuously fed into the mould as it is being manufactured.

When the product 23 that has been hydroformed is removed from the mould 19, 20, as is shown in FIG. 1, the manufacture of the tube is stopped and the tube 16 is cut by a cutting unit 24 that comprises a circular saw blade 25. The product 23 is subsequently taken away on a output unit 26, when it has been cut off. When the product 23 has been removed from the mould, the mould can be closed around the tube 16 as is shown in FIG. 1 and the tube inside the mould can be hydroformed. The product 23 is shown in FIG. 1 before it has been cut away, while it is shown in FIG. 2 after being cut away.

The hydroforming process is best described with reference to FIG. 3, which shows a closed mould 19, 20 with a newly formed product 27. A conical steel ring 30 is located at the inlet side of the mould that fits together with the inner wall of the tube 16 and that is fixed in an axial direction while having a certain amount of elasticity in a radial direction, mounted on a holder with the form of a tube 31 with spokes 29. The steel ring 30 allows the tube to glide in through the ring during manufacture of the tube, and the spokes 29 allow the ring to expand. A rod 32 extends in through the tube 31 and the steel ring 30, and this rod carries a conical plug 33, which may be made of steel. As FIG. 1 makes clear, a holder 34 is located where the tube 16 has not yet been welded closed, such that the holder can support the tube 34 and the rod 32. The roll-forming unit thus has its final shaping location after the holder in order to close the tube profile 16, although this final shaping location is not shown in the figures.

A conical steel ring 35 and a conical plug 36 are located also at the other end of the mould 19, 20. The plug 36 is attached to a rod 37, and a supply channel 38 for pressure medium extends through the rod and the plug. The plug 36 and the steel ring 35 are supported by an arm 39 that can be pivoted around an axis I, as is shown in FIG. 2. The arm 39 is not displayed in FIGS. 1 and 3. It supports the ring 35 in the same manner as the tube 31 supports the ring 30. The arrangement that is formed by the items 35-39 is shown in FIG. 2 with the plug and steel ring pivoted into the end of the tube 16. The dashed lines show the arrangement 35-39 when it is pivoted away. It is possible as an alternative to supply pressure medium through the other conical plug 33.

In order to place the tube 16 under pressure while it is in the mould 19, 20, the rods are drawn outwards by a power unit such that the plugs 33, 36 reach an initial position at which they form a seal with the rings 30, 35 and at which they elastically expand the rings to an initial position at which they make a seal with the tube 16. It is an advantage if the rings expand to form a seal since this minimises leakage and provides initial friction against the tube 16, but this is not absolutely necessary. The pressure medium is supplied through the channel 38 and the pressure of the medium provides an outwards force on the plugs 33, 36 that interact with the rings in an expansive direction such that they obtain an increased normal force onto the tube 16, which is radially supported against the mould 19, 20. The spokes 29 allow this expansion of the ring 30, and the ring 35 is expanded in the same manner. Self-locking of the end-seals is obtained in this way, and it is not necessary to apply as great an external axial force in order to obtain a seal. The arrangements for sealing the ends are thus small, simple and cheap, and they simplify the construction of the production line. The machine-operated arrangements for controlling the rods 32, 34 are not shown. When the pressure is released and the plugs 33, 36 are displaced inwards by the rods 32, 37, the rings 30, 35 shrink elastically and the unit 35-39 can be pivoted out to the position shown by dashed lines in FIG. 1. The mould 19, 20 can now be opened again, and the roll-forming unit can again push the tube 18 into the mould and push the formed product out from the mould.

The plugs 33, 36 and the rings 30, 35 are both shown as having conical form. It may, however, be sufficient with either the ring or the plug having a conical form, although the illustrated embodiment is preferred.

A suspension of oil and water may be used as pressure medium in the conventional manner.

It will be understood that the manufacturing process provides a simple opportunity for complete automation from unrolling of the steel strip to removal of the completed hydrostatically formed product.

Both the roll-forming and the hydroforming are established technology and are therefore not described in more detail. It is not necessary that the roll-formed tube have a circular cross-section; it can have any cross-section. Nor does it need to have a cross-section that is constant along its length, on the condition that the available rollforming unit can shape such tubes 

1. A hydroforming unit comprising a mould (19,20) that can be opened and sealing arrangements (30-33; 35-39) for sealing the ends of a tube-formed blank (16) placed in the mould, characterised in that each one of the sealing arrangements (30-33; 35-39) comprises a ring (30, 35) with a thin wall that fits into the inner surface of the tube (16), and a plug (33, 36) that can be displaced in an axial direction mounted axially inside of the ring, at least one of the ring and the plug having a conical form such that the plug and the ring together form a seal that is self-locking inside of the tube (16).
 2. A hydroforming unit according to claim 1, characterised by an arrangement (32,37) for initially drawing the plug (33, 36) outwards to put the ring under elastic tension against the inside of the tube-formed blank. 